(1) Field of the Invention
This invention relates generally to food compositions and, more particularly, to novel baby food compositions comprising egg yolk and to methods of making and using the compositions.
(2) Description of the Related Art
The .omega.-3 fatty acid, docosahexaenoic acid (DHA), has been shown to be a required nutrient for optimal maturation of visual and cortical function in human infants. See, for example, Hoffman et al., Am. J Clin. Nutr. 57(suppl.):807S-12S, 1993; Makrides et al., Lancet 345:1463-1468, 1995. Although the minimum dietary amount of DHA required by infants has not been unequivocally established, the Food and Agriculture Organization and World Health Organization recommend 40 mg/kg body weight for preterm infants and 20 mg/kg for term infants. (FAO/WHO Expert Consultation on Fats and Oils in Human Nutrition, FAO 1994, Rome, pp. 52-55) For term infants this is about 140 mg at birth in about 420 calories and 280 mg at 6 months of age in about 700 calories.
Breast-fed infants receive DHA in their mother's milk, which contains a full-complement of both .omega.-6 and .omega.-3 polyunsaturated fatty acids. Hoffman et al, supra; Makrides et al., supra; Innis et al, Am. J Clin. Nutr 60:347-352, 1994. However, the concentration of DHA in breast milk can vary substantially depending upon the amount of preformed DHA from meat and fish in the mother's diet. Id. In addition, many infants are not breast-fed or are breast-fed only for a few weeks and must rely on infant formula and solid baby food for their nutritional requirements.
Current infant formulas available in the United States do not contain DHA. Jensen et al., J. Pediatr 131:200-209, 1997. Furthermore, solid foods fed to babies generally have little or no DHA so that the intake of fat from such solid foods does not increase plasma DHA levels as does breast feeding. Luukkainen, supra. Thus, it would be desirable to increase the dietary intake of DHA in babies and one way to accomplish this would be to increase the amount of DHA either in infant formula or in solid baby food compositions.
Sources of DHA that have been added to infant formula to increase the content of DHA include marine oil, extracted egg yolk lipids and lipids derived from animal tissue phospholipids. U.S. Pat. No. 4,670,285, Uauy, et al., J. Pediatr. 134:612-620, 1994; Makrides et al., supra; Carlson, J. Nutr.:126:1092S-1098S, 1996. However, marine oil tends to have a strong fishy taste and odor and thus is unsuitable for adding to infant formula or solid baby food. In addition, lipids extracted from egg yolk and animal tissue are susceptible to oxidative deterioration. Also, with respect to solid baby food preparations, production of fish and/or animal oils requires extensive processing, so that the use of such processed oils in a baby food composition would diverge from the "whole food" and "natural food" concepts of baby food which is popular among caregivers.
One possibly suitable source of DHA that might be incorporated into a solid baby food preparation is whole egg yolk. Although, hens' eggs ordinarily contain only very low amounts of DHA, hens fed a diet enriched with DHA or DHA precursor can contain about 80 mg/egg yolk or about 10 mg/gram of egg yolk solids. see Table 1, infra. Such DHA-enriched eggs have been developed as sources of DHA for human consumption. Herber et al., Poultry Sci 75:1501-1507, 1996; Oh, U.S. Pat. No. 5,415,879. Nevertheless, this earlier work provided no suggestion as to how such DHA-enriched eggs might be incorporated into an acceptable semi-solid baby food preparation.
Some semi-solid baby food compositions containing egg yolk solids are currently available in the United States while others are known to have been available in the past. However, such compositions have contained either a small amount of egg yolk solids, i.e. less than 5%, or a large amount of egg yolk solids, i.e. about 29% to 30%, neither of which is satisfactory as a food source for supplementing the infant diet with DHA. The compositions containing less than 5% egg yolk solids contain insufficient amounts of egg yolk solids to serve as a delivery vehicle for increasing DHA in the diets of infants even if DHA-enriched eggs were used in the formulations. Such formulations would be unable to provide the 140 to 280 mg/day required during the first 6 months of life in a 113-gram serving contained in a standard jar of baby food. Although compositions containing 29% egg yolk solids could provide a significant amount of DHA in a single serving of 113 grams if made with DHA-enriched egg yolk solids, these egg yolk-rich baby foods are no longer sold in the United States, in large part due to their extremely poor taste. Indeed, it is well known that infants typically reject cooked egg yolk, probably because of its strong taste and gritty, mealy texture. Thus, there remains a continuing need for a semi-solid baby-food composition containing a natural source of DHA in a composition suitable for feeding to babies.